In situ combustion production method

ABSTRACT

A METHOD FOR RECOVERING HYDROCARBONS FROM A SUBTERRANCEAN HYDROCARBON-CONTAINING FORMATION BY COUNTERFLOW IN SITUCOMBUSTION WHEREIN THE OXIDANT IS PASSED THROUGH COATED CHANNELS FROM THE INJECTION WELL TO THE COMBUSTION ZONE TO   PREVENT SPONTANEOUS IGNITION OF IN PLACE HYDROCARBONS AT UNDESIRABLE LOCATIONS.

United States Patent 2,917,296 12/ 1959 Prentiss inventor Harry W.Parker Bartlesville, Okla.

Oct. 27, 1969 June 28, 1971 Phillips Petroleum Company Appl. No. FiledPatented Assignee 1N SlTU COMBUSTION PRODUCTION METHOD 5 Claims, 1Drawing Fig.

U.S. C1 166/259, 166/261 Int. Cl E21b 43/24 Field of Search 166/259,256,261, 302, 251

References Cited UNITED STATES PATENTS 2,962,095 11/1960 Morse 166/2593,004,594 10/1961 Crawford 166/259 3,010,513 11/1961 Gemer 166/2593,115,928 12/1963 Campion et al..... 166/259 3,135,324 6/1964 Marx166/261X 3,221,812 12/1965 Prats 166/261 3,314,476 4/1967 Staples et al.166/260 3,342,261 9/1967 Bond 166/259 3,368,622 2/1968 Klein et a1166/261 3,385,362 5/1968 Strange et a1 166/259 Primary Examiner-StephenJ. Novosad Anorney- Young and Quigg ABSTRACT: A method for recoveringhydrocarbons from a subterranean hydrocarbon-containing formation bycounterflow in situ combustion wherein the oxidant is passed throughcoated channels from the injection well to the combustion zone toprevent spontaneous ignition of in place hydrocarbons at undesirablelocations.

PATENTED JUN28 197i 3; 5817-38 INVENTOR. H. W. PARKER BY Q M as A 7'TORNE V5 IN SITU COMBUSTION PRODUCTION METHOD This invention relates toan in situ combustion method for producing hydrocarbons from asubterranean formation. In another aspect, this invention relates to amethod for supply ing oxidant to a combustion zone of a counterflow insitu combustion operation for producing hydrocarbons from a subterraneanformation and preventing spontaneous combustion of the in placehydrocarbons at undesirable locations. The counterflow in situcombustion process referred to herein is sometimes referred to as theinverse, countercurrent," or reverse combustion process.

In situ combustion is commonly used to facilitate production of viscoushydrocarbons which are not readily produced by conventional productionprocedures. Typically, an in situ combustion arrangement may include aninput or injection well for the introduction of oxygen-containingcombustionsupporting fluid, such as air, and an output well for theremoval of the desired hydrocarbons. Each of these wells extend from thesurface of the earth into the formation desired to be produced. In themore conventional forward or direct in situ combustion process, acombustion front is initiated in the formation desired to be producedaround the input well and combustion-supporting fluid is continually fedinto the formation and to this front through said input well. Thecombustion front provides a radially expanding source of heat andfunctions to distill and reduce the viscosity of hydrocarbons in theformation ln the latter state, the hydrocarbons are capable of morefreely moving through the formation to the input well where they may berecovered by conventional production means. In addition to creating theexpanding source of heat, the combustion-supporting fluid is convertedto hot combustion products that move away from the input well toward theoutput well while transporting reservoir hydrocarbons.

When used in formations containing very viscous hydrocarbons, theforward or direct combustion process often proves unsuccessful becauseof the buildup of a relatively immobile bank of viscous liquidhydrocarbons in the formation beyond the combustion front. This bankfunctions to seal the formation around the combustion front and thusimpedes, or restricts completely, the flow of combustion-supportingfluid from the input well and through the formation. As a result, thecombustion front dies and the recovery process becomes completelyineffective. In order to avoid the viscous hydrocarbon buildup problemencountered in the forward combustion process, the aforementionedcounterflow combustion process has been developed. The counterflowcombustion process is similar to the forward combustion process in thatit utilize input and output wells extending from the surface of the caninto the formation desired to be produced and also utilizes a combustionfront in the formation to decrease the viscosity of hydrocarbonstherein. The counterflow combustion process differs from the forwardcombustion process primarily in that the combustion zone is initiatedinto the formation around the output well rather than the input well.

Typically, in application of the counterflow combustion process,combustion is initiated around the output well by heating the formationand injecting an oxidant, such as air, into the heated area. Initially,the oxidant may be injected through either the input or output well.After combustion is initiated, however, the injection through the outputwell is terminated and the oxidant is introduced into the formationthrough only the input well. When the process is in operation thecombustion zone moves radially outward from the output well while beingsupplied with oxidant, and possibly fuel, from the input well. From thelatter relationship, the process derives the name of counterflow,inverse, reverse, or countercurrent combustion, since the combustionfront moves in a reverse direction to that in the forward combustionprocess and in a direction countercurrent to the direction in which theoxidant moves. It is noted that in aforedescribed forward combustionprocess the combustion front and the oxidant move in the same direction.

The oxidant introduced through the input well in the countercurrentcombustion process functions to drive hydrocarbons is not impeded by theformation of a heavy blank of viscous hydrocarbons near the combustionfront, since hydrocarbons upstream from the combustion front remainrelatively cool and those downstream from the front are maintained at alow viscosity by the preheated formations around the output well.

The application of the countercurrent combustion process, however,presents a spontaneous ignition problem that is not encountered in aforward combustion process. Specifically, in the countercurrentcombustion process it has been discovered that spontaneous ignition willtake place in portions of the formation upstream from the advancingcombustion front. Spontaneous ignition results from the slow oxidationof organic matter (in this case the crude within the formation beingproduced) by the oxidant as it flows through the formation from theinjection well to the combustion front. This slow oxidation generatesheat that increases the temperature of the formation. As the temperatureincreases, the rate at which the oxidation occurs increased until thetemperature is sufficiently high that all, or nearly all, of the oxygenin the oxidant is consumed before it reaches the combustion front. Whenthis occurs, there is little or not oxygen available to support thedesired countercurrent combustion front, and as a result this front diesout. At or near this time, the portions of the formation remote from theoutput well and generally near the injection well, reach a temperaturesufficient to support spontaneous ignition and thus a new and undesiredcombustion front is created. Typically, this front will form around theinjection well and create, in effect, a direct combustion process.

The timerequired for spontaneous ignition within the formation isaffected by such things as the character of the crude, the oxygencontent of the oxidant, the rate of oxidant injection, and the reservoirtemperature and pressure. The most controlling factor, however, is theambient temperature of the reservoir. For nearly all reservoirs, but themost shallow (i.e., less than 500 feet from the surface), the ambientreservoir temperature will be sufficiently high (i.e., F. or above) topromote spontaneous ignition near the injection well within a relativelyshort time, for example, in the order of 3 months.

Therefore, since countercurrent combustion operations are usuallyplanned to last for periods ranging in years, it can be seen thatspontaneous combustion in areas of the formation remote from the desiredcountercurrent combustion zone is likely to occur. With this occurrence,the combustion zone around the output well will die out and a newcombustion zone will form around and spread radially from the inputwell, thus creating a direct combustion process. This direct combustionprocess will, in turn, be accompanied by the aforediscussed problemsencountered in conventional direct combustion processes. Thus, incountercurrent combustion processes, it has been found to be highlydesirable to control the rate of oxidation in the formations upstreamfrom the combustion zone to prevent spontaneous ignition within thoseportions of the producing formations.

It is therefore an object of this invention to provide an improvedcountercurrent in situ combustion production method. Another object ofthis invention is to provide a countercurrent in situ combustion processthat will not permit spontaneous ignition of the in place hydrocarbonsat undesirable locations. Yet another object of this invention is toprovide an in situ combustion process that requires less equipment,labor, and power. Other aspects, objects, and advantages of the presentinvention will become apparent from a study of the disclosure, theappended claims, and the drawing.

The drawing shows the formation, wells, and a portion of the equipmentutilized in the countercurrent in situ com bustion production method ofthis invention.

In the drawing, at least one injection well 2 and one production well 4extend from the surface of the earth downwardly through a subterraneanhydrocarbon-containing formation 6. The injection well 2 and productionwell 4 are laterally spaced one from the other. The injection well 2preferably has casing set through the production zone 6 with said casingaffixed to said formation 6 to form a fluidtight seal. The casing of theinjection well 2 is thereafter opened into the adjacent formation 6 at aposition preferably an equal distance from the top and bottom 8, 10 ofthe hydrocarbon-containing fonnation 6 in order to assure substantiallyequal oxidant flow in both an upward and downward direction at thecombustion zone (to be later described). A fracture 11 is formed byhydraulically fracturing methods known in the art from the opening inthe injection well 2 through the hydrocarbon'containing formation 6 to alocation adjacent a remote production well 4.

In order to provide additional protection against spontaneous combustionin the vicinity of the injection well 2, it is preferred that a gelledfluid bank 12 be formed within the formation 6 surrounding the injectionwell 2 over the entire thickness of the formation. The gelled fluid bank12 can be formed by slowly injecting a volume of gelled fluid into thewell 2 prior to forming the fracture 11. The gelled fluid bank 12 can bemaintained during in situ combustion operations by periodicallyinjecting slugs of gelled fluid into the formation 6. Gelled fluids thatcan be used with the method of this invention are, for example:solutions containing guar gum, polysaccharides, sodium silicate, and thelike that raise the viscosity of the fluid to above 100 cp. Antioxidantscan also be incorporated with the gelled fluid to protect againstspontaneous combustion.

The surfaces of the fracture 11 extending through the fracture 6 arecoated by injecting into the fracture 6 a fluid loss additive. Theparticles of the fluid loss additive adhere or are held by pressureagainst the surfaces of the fracture l1 and form a sealed coating 14over preferably the entire surface of the fracture 6. The coating 14preventsin place hydrocarbons from flowing into the fracture and oxidantthat is to be passed through the fracture 6 from moving through thefracture surfaces and into the formation 6 at locations between theinjection well 2 an the combustion zone 16 that is to be established.The fluid loss additive mixtures for use in coating the fractures inthis invention can be, for example, mixtures of water, etc., with fluidloss additives such as cornstarch, wheat flour, gluten,carboxymethylcellulose, hydrolyzed polyacrylonitrile, and the like.

Examples of the fluid loss mixtures to be used are as follows:

FLUID LOSS MIXTURES The volume of mixture used is dependent upon thetotal surface area of the fracture desired to be covered. A recommendedvolume would be, however, 500 to 2000 bbls.

A combustion zone 16 is thereafter formed across preferably the entirethickness of the production formation 6 contiguous to the productionwell. That combustion zone 16 is formed by igniting the in placehydrocarbons by various methods known in the art. An oxidant, preferablyair, is then injected downwardly through the injection well, through thecoated fracture, and to the combustion zone 16 for supplying oxygen'tothe combustion zone and moving said zone through thehydrocarbon-containing formation 6. The pressure within face.

By providing a coating to the fracturesurfaces for separating andmaintaining the oxidant from substantial contact with the in placehydrocarbons during flow of the oxidant through the fracture 11 to thecombustion zone, the occurrence of spontaneous combustion at undesirablelocations within the formation 6 is greatly reduced. To further reducethe occurrence of spontaneous combustion it is preferred that theoxidant be cooled to a temperature at least below F. prior to injectingsaid oxidant into the injection well. The oxidant can be cooled bycooling apparatus 18 such as a refrigeration system, cooling fins, heatexchangers, and other like methods known in the art. It is important,however, that the oxidant be cooled by the cooling apparatus 18 to atleast 90 F. since heat is added to the oxidant by increasing thepressure on the oxidant sufficient to deliver said oxidant to thecombustion zone 16 and by conduction of heat from the reservoir 6 to theoxidant as said oxidant passes through the fracture. So cooling theoxidant to below 90 F. assures that the oxidant passing through thefracture is at a temperature lower than the adjacent formation 6 andthereby continually cools and assists in preventing spontaneouscombustion at undesirable locations.

By preventing mixing of oxidant and in place hydrocarbons and coolingthe formation by the method of this invention, countercurrent in situcombustion can be conducted without the danger of spontaneous combustionat undesirable locations.

Other modifications and alterations of this invention will becomeapparent to those skilled in the art from the foregoing discussion andaccompanying drawing and it should be understood that this invention isnot to be limited thereto.

1 claim:

1. A method of recovering hydrocarbons from a subterraneanhydrocarbon-containing formation penetrated by at least one injectionwell and one production well spaced from said injection well,comprising:

forming a fracture through the hydrocarbon-containing formation from aninjection well to a location adjacent a remote production well; coatingthe surfaces of the fracture with sealing material; establishing acombustion zone in a portion of the hydrocarhon-containing formationcontiguous to the production well;

injecting an oxidant downwardly through the injection well, through thecoated fracture and to the combustion zone for supplying oxygen to thecombustion zone and moving said zone through the hydrocarbon-containingformation; and

lowering the pressure within the production well and producing fluidsentering said production well.

2. A method, as set forth in claim ll, including cooling the oxidant toa temperature at least below 90 F. prior to injecting said oxidant intothe injection well.

3. A method, as set forth in claim 1, wherein the surfaces of thefracture are coated by injecting a mixture of water and fluid lossadditive downwardly through the injection well and outwardly through thefracture.

4. A method, as set forth in claim 1, including injecting a volume ofgelled fluid into the formation adjacent the injection well prior tofracturing the injection well and maintaining the bank of gelled gelfluid around portions of the injection well in thehydrocarbon-containing formation by periodically injecting slugs ofgelled fluid into said formation.

5. A method, as setforth in claim 1, wherein the oxidant is air.

